Simple phthalocyanines are generally solid compounds of dark green color, having a high melting temperature and a very low solubility in organic solvents. It is hence very difficult to prepare polyphthalocyanines of high molecular weight or to use this type of polymer in their final cyclized form. On the contrary, the cyano-addition reactions may be used to cross-link monomers or easily melted and soluble oligomers, the cross-linking reactions being performed by mere heating at the moment of use of the products.
Such cyano-addition reactions have been disclosed with aromatic or arylaliphatic compounds containing amides, azomethines or ethers chainings (Walton and Griffith: Applied Polymer Symposium, 1975, 26, 429; Polymer Science and Technology, 1975, 9B, 665; ACS Division of Organic Coatings and Plastics Chemistry, 1978, 38, 596. Keller and coll., SAMPE Quaterly, July 1981, P.1). In these publications and in U.S. Pat. Nos. 4,056,560, 4,057,569, 4,102,873, 4,116,945, 4,136,107, 4,209,458, 4,223,123, 4,234,712 and 4,238,601, the formation of phthalocyanines is described as a very slow reaction which, in the absence of metal salts, may last several hours and sometimes several days at a temperature generally ranging from 200.degree. to 300.degree. C. Moreover, Marullo and Snow (ACS symposium series, vol. 195, 1982, p. 325) have shown that the selectivity of the reaction of phthalocyanine formation is very low and that the cross-linked lattice is in fact a complex mixture containing several types of hererocyclic systems. Finally, the thermal stability of the thermoset resins is limited by the nature of the starting molecules.
In order to increase the thermal stability of phthalocyanine resins, highly thermostable heterocyclic structures such as for example, aromatic imides, can be introduced in the macromolecular chain. But polyimides, even as oligomers of low molecular weight, have too high a melting temperature and too low a solubility to form good precursors of polyphthalocyanines.